1. Field of the Invention
The present invention relates to improvement in the traditional HF cleaning method of silicon wafers (hereafter simply referred to as wafer).
2. Description of the Prior Art
The traditional HF (hydrofluorid acid) cleaning was well used in a cleaning process due to its high ability to remove metallic ions on the surface of a wafer. However, it has a problem that wafers are easily subject to particle contamination in an operation of its own and thus the cleaning in an aqueous solution of hydrochloric acid and hydrogen peroxide combined is preferred when particle contamination is to be avoided. Particles on a wafer cause such a disadvantage that, in optical exposure by a stepping projection aligner in fabrication of electronic devices, the particles intercept light beam through the windows in a mask to make shadows on a photoresist layer, which results in much of decrease in device production yield due to occurrence of defective interconnections directly related to the shadows or poor local exposure. What's more, under the recent trend towards more highly packed devices in a silicon IC chip, the level down of metallic ion presence on a wafer has been increasingly required, which naturally calls for introduction of a new improved HF cleaning with the intrinsic nature of less particle contamination thereof.
The inventors have continued in-depth research on decrease in particle contamination of the HF cleaning of wafers and found that it is important for decrease in particle contamination of wafers in an HF cleaning how to take them in or out a hydrofluoric acid bath (hereinafter referred to as HF bath) and a deionized water bath for rinsing the wafers, which is the clue from which the present invention has been made.